1. Field of the Invention
The present invention relates to fuel cell systems and operating methods thereof. More specifically, the present invention relates to a fuel cell system that controls a re-starting operation of the fuel cell after a rollover of the fuel cell, and an operating method thereof.
2. Description of the Related Art
Direct methanol fuel cell systems are superior to other fuel cell systems in terms of their smaller size and lighter weight, and are used suitably for riding-type vehicles such as motorbikes.
In direct methanol fuel cell systems, an electrolyte film provided by a solid polymer film is provided in the fuel cell. Aqueous methanol solution is supplied by an aqueous solution pump from an aqueous solution tank to an anode of the fuel cell and simultaneously, air which contains oxygen is supplied to a cathode by an air pump. After the reactions in the fuel cell, unused methanol, water and carbon dioxide are discharged from the anode and returned to the aqueous solution tank while unused air and water are discharged from the cathode and are supplied to a water tank. In the aqueous solution tank, carbon dioxide is separated from liquid whereas unused air is separated from liquid in the water tank.
Generally, when the direct methanol fuel cell system as described is tilted excessively due to a rollover or the like, the following problems arise. For example, exhaust pipes for the gas/liquid separation in the water tank and in the aqueous solution tank are blocked, disabling the gas/liquid separation, or air is trapped in the aqueous solution pump, disabling circulation of the aqueous methanol solution. These events make impossible to continue power generation, causing problems such as unnecessary consumption of electric power by the system components. A problem also occurs in fuel cell systems that use hydrogen as the fuel. In this case water is trapped in the cathode.
JP-A 2004-111212 discloses a fuel cell system that detects a rollover with a tilt sensor and is capable of stopping the system when a rollover is detected. This enables to prevent unnecessary use of electric power.
However, JP-A 2004-111212 does not disclose a detailed method of re-starting after the stoppage due to rollover, mentioning only that system status is checked before the re-start.
A rollover can cause problems. For example, water and aqueous methanol solution are trapped on the cathode side, aqueous methanol solution on the anode side drains and the electrolyte film is dried. These problems pose difficulties in the subsequent re-start, but nothing is disclosed about how these problems may be solved.